Method and device for overlapping welding of two coated metal sheets with a beam of high energy density

A lap welding process for welding, by means of a high-energy-density beam (11), two metal sheets (1, 2) coated with a material that has an evaporation temperature below the melting point of the material of the sheets, characterized in that the two coated sheets (1, 2) are at least partly overlapped;

• the faces of the two sheets (1, 2) in the overlap region are brought into contact with each other;
• the high-energy-density beam (11) is split, on the one hand, into a first sub-beam (12) fully penetrating both coated sheets (1, 2) in the overlap region and forming a first weld pool (18) in this region and, on the other hand, into a partially penetrating second sub-beam (13) forming a second weld pool (19), the depth of which is less than the thickness of the upper coated sheet (1), the second weld pool at least partly overlapping the first weld pool (18) in order to promote removal of the coating material vapor;
• an inert gas jet (21) is directed with a high ejection velocity onto the second weld pool (19) in order to form a depression (22) in the surface of the second weld pool (19), increasing the rate of removal of the coating material vapor;
• and
• a hermetically sealed continuous weld bead or seam (5) is formed along the overlap region by displacement of both sub-beams (12, 13) and the inert gas jet (21), or of both coated sheets (1, 2).